1. Field of the Invention
The present invention relates to an automatic balancing mechanism for use with a medical stand apparatus, which is capable of advancing and holding heavy devices such as an operating microscope and its auxiliary devices at a desired spatial position during microsurgery.
2. Prior Art
Microsurgery is known particularly in the fields of brain surgery and cardiac surgery using a operating microscope as a "medical optical device" for viewing and inspecting a part to be treated during the operation. Various stand apparatuses are available for holding at a desired spatial position the heavy devices such as an operating microscope and its auxiliary devices. A typical type of the stand apparatus comprises a retaining link mechanism of parallel link pivotally (or tiltably) mounted at the middle to a support base, an operating microscope mounted to one end of the retaining link mechanism, and a counterweight mounted to the other end of the retaining link mechanism for countervailing the weight of the operating microscope relative to the pivot thereof
In common, the stand apparatus of the balancing type is installed at an optimum position in an operation room depending on the content of the surgery to be carried out and balance adjustment is performed. The operating microscope is provided with various auxiliary devices including a side microscope for an assistant doctor and a video camera. The balance on the stand apparatus should be adjusted between the counterweight and the operating microscope with its auxiliary devices, with the counterweight shifted in accordance with the operating microscope and auxiliary devices if any.
It is essential for retaining the operating microscope and its auxiliary devices at a desired position in the space to balance in both the horizontal direction (when gravity acts vertically) and the vertical direction (when an imaginary direction where gravity acts horizontally). Otherwise, when the parallel link mechanism is biased, the weight balance will be lost and fail to retain the operating microscope at the desired spatial position. For making the balance, two counterweights are conventionally provided for controlling in both the vertical and horizontal directions respectively or one single counterweight is adjustably moved in both the vertical and horizontal directions. However, either manner would be realized by a complicated bulky system, which will be undesirable.
I, the inventor, developed an improved type of the stand apparatus in which a retaining link mechanism carrying a microscope and its auxiliary devices is arranged movable in the vertical direction while a counterweight is arranged movable in the horizontal direction so that the balance is held in both the vertical and horizontal directions (as is disclosed in Japanese Patent Laid-open Publication No. 269463/1994.
My previous invention is actually not so satisfactory because the balance is manually adjusted in spite of its simpler construction than that of any other prior art. The balancing adjustment will hardly be automated unless modified and thus neither simpler balance adjustment nor minimization of the involving time could be achieved.
The present invention is directed towards overcoming the above drawback and its object is to provide an automatic balancing mechanism for a medical stand apparatus capable of automatically balancing an optical device for medical use and its auxiliary devices.